Magnetron



Sept. 2, 1952 J. F..HULL 2,609,522

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. VENToR. Jose F. Hu LL W uw? Sept 2, 1952 J. F. HULL 2,609,522

MAGNETRON Filed April 3, 1950 4 Sheets-Sheet 2 INVENTOR. JOSEPH F. HULL WW n mi@ Sept. 2, 1952 1 4 F, HULL 2,609,522-

MAGNETRON Filed April 3, 1950 4 Sheets-Sheet 5 final I-I 21mm. In. Hm

INVENTOR. JOSE PH F. HULL W' ww? Patented Sept. 2, 1952 UNITED STATES PTENT CFFICE i j MAGNETRON Joseph F. Hull, Neptuna'. J y Application April 3, 1950, Serial lie-153,682

Claims.

(Granted under the act of March amended April 30, 1928; 370 0.

This is the parent application of divisional application Serial No. 269,572, filed January 31, 1952. "5'

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment of any royalty thereon.

This invention relates to'electronic4 devices and more particularly to magnetrons.

In the Patent 2,454,337 which was issued to E. C. VOkress on November 23,1948, there is shown a magnetron structure employing an inverted hole-and-slo't type anode structure girdled by a cathode. In this typeof structure a number of electrical modes exist which are closeV together. Thus, such a device will tend to operate in the several different 'modes which results in reduced efficiency from this type of magnetron structure. In the conventional non-inverted wave or holeand-slot type of magnetron, mode frequency separation is accomplished by employing socalled straps which. connect alternate anode segments. However, the effectiveness of strapping is greatest for theshOrteSt strap length. Inasmuch as the magnetron anode showny in the Okress patent is inverted from the hole-and-slct anode structure of the conventional magnetron, the distance between alternate segments is too great for strapping to be electiveand su'iiicient mode separation isv difficult to achieve. If few cavities are used, the cavity structure is Vso divergent that the high current portion of the cavity occupies too small an area, thus decreasing circuit efficiency. If the number of cavities is large, the number of modes is increased, and as a result there isfinsu'icient mode frequency separation. Due tothe fact that `the interdigital magnetron is a single cavity resonator and the wave type magnetron is a multi-cavity resonator, it is easy to show Awhy the interdigital magnetron anode structure can be inverted without detrimental effects on V'mode separation and circuit efficiency. This is not true for the Wave type magnetron. Moreover, with the inverted interdigital magnetron, a large diameter cavity can be built with a large numberof segments to provide a greater area for the high current flow, and still provide suicient mode separation.

It is therefore an object of this invention to provide an improved ultra-high frequency electric discharge device of the magnetron type.A

Another object of the invention is to provide a magnetron structure wherein the resonant system permits a great degree of mode separation thus increasing the efficiency of themagnetron structure.

Still another object of the invention is to provide an inverted magnetron'structure employing aninterdigtal type anode. j.

Further objects of fthe vinvention will appear to those skilled in the art to which it pertains, b oth by .direct recitation thereof as the description proceeds and by implication from` the context. Y

Referring to the accompanying drawings .in which like reference numerals indicate similar parts throughout the several views: I

Fig.. 1 is a cross-sectional viewof a magnetron embodying the present invention; I Fig. 2 is a perspective view showing the detailed construction of the magnetron cathode and anode illustrated in Fig. 1;

Fig. 3 is a perspective view showing the, de-

tailed construction of the shown in Figs. 1 and 2; .r

Fig. 4 is a` cross-sectional View of a tunable magnetron embodying the present invention;

Fig. 5`is a perspective View ofanother embodiment of the anode shown in Fig. A3; Y l

Fig. 6 is an elevational view Vof a tunable {niagnetron employing a preferred embodiment of the magnetron anode;

Fig. '7 is a vertical cross-sectional View on an axial plane of the portion above line A- .of the magnetron shown in Fig. 6;

Fig. 8 is a vertical cross-sectional view on an axial plane of the portionv below line A-Aof the magnetron shown h'in Fgl; and

Fig.v 9 is `a perspective view showing the detailed construction of a preferred embodiment of the anode employed in the magnetron shown in Figs. 6, 7 andkB.

Referring now toFig'. l ofthe accompanying drawing, there is shown an inverted ultra-high frequency magnetron including a coppercylindrical casing or tube lil with top and bottom end plates Il and'lZ which are welded or othermagnetron anode wisehermetically sealed to theA inner surface of said cylindrical casing. i y. At approximately the central portion'of said tube there is provided an'ranode -structure i3 which is shown invv perspective detail in Figs. 2 and 3. Anode structure I'3,Vwhich Amay preferably consist of copper, may be considered as cornprising a pair of spaced annular top and bottom discs Hl and l5, which are axially aligned, and a plurality vof oppositely placed sets of uniformly spaced bars l5 extending toward each other from the outer periphery of said discs. Uniformly spaced bars I6 are circumferentially arranged around the outery ),zueriphery.Vr of said discs'in a plane perpendicular to the surfaces thereof so as to interleave with each other. Each of these bars are of uniform length and Width, the length of the bars being approximately equal to the spacing between said discs. Alternate bars such as I1 and I9 are joined to bottom disc I5 while the remaining alternate bars such as I8 and 20 are joined to top Adisc I4, so that if one goes around the anode structure in any one direction, alternate bars are joined to the same disc. These bars may be of uniform thickness but in order to achieve greater heat dissipation and higher frequency operation, these bars are tapered linearly in such a manner so that each bar is thicker at the joined end than at the opposite end thereof.

In order to support the anode structure centrally with respect to the tube,;the inner periphery of annular anode discs I4 and I5 are brazed to the outside surface of tubular member 2|, made of copper or other non-magnetic metal, which extends longitudinally from top end plate II to bottom end plate I2 through the center of the tube and is coaxial therewith. The region bounded by top and bottom discs I4 and I5, the portion of the outside surface of tubular member 2| therebetween and the interleaved bars is termed the magnetron resonant chamber.

Girdling and radially spaced from said bars is cathode 22 which is coated with an emissive material and which is held in position by channel housing 23. Said channel housing consists of lateral cylindrical wall 24 and top and bottom end discs 25 and 26. The inner periphery of top and bottom end discs 25 and 26 of said housing extend radially inward slightly beyond the circumferential emitting surface of cathode 22, as shown in Fig. 2, in order to provide cathode end shields, thus preventing electron leakage from the interaction space between bars I6 and cathode 22. y

Within said channel Vhousing and juxtaposed with said cathode there is provided a heater coil 21, one end of which is welded to channel housing 23. The other end of coil 21` is insulated from channel housing 23 and is connected to end conductor 29 which extends through lateral wall structure of casing I9, and is supported coaxially in glass seal 33. Cylindrical heat shields 32 are provided within channel housing 23 between cylindrical wall 24 and heater coil 21. End conductor 28 which is welded to channel housing 23 also extends through lateral structure of casing III and is supported coaxially in glass seal 3|. The direct-current high potential 35 is applied in the usual manner through end conductor 28 and alternating-current heater coil potential 36 is supplied between end conductors 28 and 29 to supply the heater current.

Within tubular member 2| and coaxially therewith is an inner conductor 31 which extends approximately half the length of the upper portion of said tubular member. A coupling loop 38 is located within the resonant chamber and has a stem extending .radially inward through a hole 39 in tubular member 2|, and connects with the lower end of inner conductor 31. Thus, eectively, tubular member 2| and inner conductor 31 comprise a coaxial output line for the magnetron. Door knob coupler 4B connects with the upper end of inner conductor 31 in order to couple radio frequency energy to output waveguide 4|.

Water or other liquid cooling of the anode structure may be effected by the provision of rigid inlet and drain pipes 4| and 42, respectively, which are arranged within the lower portion of tubular member 2| as shown. Water stopper plug 43 is positioned within tubular member 2| between the lower end of inner conductor 31 and the upper end of inlet pipe 4I in order to prevent uid from entering into the resonant cavity. Water ows continuously through inlet pipe 4I and the overflow is removed through drain pipe 42. Thus, at all times a jacket of water is provided in the lower portion of tubular member 2| between plug 43 and drain pipe 42 to dissipate the heat generated in anode structure I3;

In order to provide a uniform magnetic eld, the magnetron of the present showing is provided with ring-like magnetic coils 44 which are conveniently situated exterior to casing Ill. Girdling and radially spaced from the outer periphery of said coils is a cylindrical iron casing 45 which is joined to bottom end plate|2 of tube |0 by means,` of studs 46 and 41. Holes are provided in said iron shell to provide convenient access to end conductors 28 and 29.

In order to provide radio frequency chokes to further decrease the leakage of electromagnetic energy from the resonant chamber, there are provided a pair of cylindrical ironA sleeves 48 and 49 which depend from the inner periphery of top and bottom end plates II and I2, respectively. Said sleeves respectively girdle the upper and lower portion of tubular member 2|- and are coaxial therewith, and extend inwardly from both top and bottom members toward the anode for a distance approximately 1A wave length of the operating frequency. The outer diameter of said sleeves are approximately equal to twice the diameter of the tubular member 2|.

That portion of the top and bottom end plates I I and I2 between the sleeves and tubular member 2| is composed of copper or any other suitable non-magnetic material, while the remainder of the top and bottom end plates is composed of iron. In this manner, the magnetomotive force is applied close to the region of the interaction space in order to minimize magnetic iiux leakage. Thus, a uniform magnetic field is effectively applied to the interaction space in the proximity of anode I3.

The combined inuence of the uniform magnetic field established by the coils 44 over the interaction space, the direct current electrical eld due to the voltage applied between anode I3 and cathode 22 and the potential due to the space charge cloud of the electrons, cause the electrons emitted from cathode 22 to migrate between said cathode and anode in a circumferential path coaxial with the anode. Simultaneously, as the electrons are rotating, the anode segments are individually assuming a sinusoidal time varying potential such that each anode segment is electrical degrees out of time phase with each adjacent segment. 1f the rotational velocities of the electrons are such that any one individual electron is always under a positive segment, synchronization is said to occur, that is, the electrons are keeping step with the electric eld of the anode structure. It is well known that when said synchronization occurs, magnetron oscillations may be generated provided voltage and magnetic field are of proper value for the particular mode of operation which inthe present instance is the one known in the art as the 1r mode.

In Fig. 4 there is shown a magnetron emplying an anode I3 which differs from the anode shown in Fig. 3, only in that bottom anode disc 5 is axially movable for tuning the magnetron. The means for axially moving disc l5 consists of two rods 56 and 5| which extend through sleeve G9 and sealing bellows 52 to ball bearing knurled nut 53. Cylindrical choke 54 is'providedtc prevent leakage of electromagnetic energy from the interaction space. As shown in Fig. 5, the interleaved bars of anode I3, in addition to being tapered as shown in Fig. 3, may also be circumferentially tapered so that the teeth are wider at the joined ends than at the opposite ends thereof in order to achieve a wider tuning range.Y Figs. 6, 7 and 8 illustrate a'tunable magnetro employing a preferred modification of the anode structure which is shown in detail in Fig; 9.

The tunable magnetron shown in Figs. 6, -7 and 8 includes an anode structure I8 which is axially mounted within nommagnetic metallic shell I II, this shell being welded to upper pole piece I I2 as well as lower pole piece I |3, as illustrated at jl'IlI, H5, ||6 and Il respectively. As shown in Fig. 9, anode structure |I|| `consists 0f a plurality of axially aligned annular discs having uniform outer diameters which are `stacked one above the other and are equi-distantly spaced from each other. With the exception of upper and lower anode end discs H8 and II3, the inner diameter of the intermediate anode annular discs such as I 28, |23 and |25 are also uniform. Circular shaped cut-outs |2I are circumferentially and uniformly spaced around the outer periphery of each of said discs, thus providing uniformly spaced teeth |22. Said discs are positioned one above the other so that the teeth ci' only alternate discs such as |23 and |25 and |24 and |26 are coplanar. As illustrated, bars |27 are in abutment with said coplanar teeth, one bar for each vertical row of coplanar teeth. Each of these bars are of uniform length, width and thickness, the length of the bars being substantially equal to the spacing between upper and lower anode end discs IIB and I I5.

Girdling and radially spaced from bars |2'| is a cathode 22 which is coated with an emissive material on its inner surface and which is heldin position by channel housing 23, said housing consisting of lateral outer cylindrical wall 24 and top and bottom end discs 25 and 26. The inner periphery of top and bottom end discs 25 and 26 of said housing extend slightly beyond the circumferential emitting surface of cathode 22 in order to provide cathode end shields, thus preventing electron leakage from the interaction or discharge space |23 cf the magnetron between coplanar bars |22 and said cathode.

Channel housing 23 is rigidly held in place by three supporting rods, one of which is illustrated at |23, one end of each of said rods being welded to disc 25 and the other end being welded or brazed to inner metal casing |33 which is encompassed by outer ceramic shell |3|. Said shell is brazed to upper pole piece ||2 as illustrated at |32 and |33. Both the inner casing |30 and the outer ceramic shell are hermetically sealed by annular cap |34.

Within said channel housing and juxtaposed with cathode 22 there is provided an insulated heater coil 2l, one end of which is welded to channel housing 23. The other end of coil 2l is insulated from channel housing 23 and connected to end conductor |35 which extends through hole in cap |34 and is supported coaxially therein by glass seal |36. The direct-current high potential |31 is applied in the usual manner through end cylindrical conductor |38 and alternating-current heater coil potential |39 is supplied between end conductors |35 and |38 to supplyheater current.

In order to support anode structure III) centrally with respect to cathode 22 and shell the inner diameters `of all the stacked lannular discs, with the exception of upper and lower anode end discs |I8 and |19, are brazed 'to the outside surface vof cylindrical casing |43 which is coaxial and concentric withshellV I I. The inner diametersy of anode end discs IIS and I|9 are slightlylarger than the inner diameters of the intermediate annular discs. Tubular .members |4| and |42 are brazed to the inner diameters of end discs I I8 and I I9, respectively, said tubular members being concentric and coaxial with cylindrical casing |46. Tubular members I4| and m2 will yhereinafter bereferred to as the upper tubularmember and as the lower tubular member, respectively. Thus, effectively, upper and lower tubular members |4| and |42 are the outer conductors of a coaxial line, the inner conductor of which consists of the outer surface of cylindrical casing |48.

Positioned ybetween the innere wall of upper tubular member I4| and the outer wall of cy1indrical member |46 is a cylindrical sliding contact |43 which is adjustable for tuning the magnetron. Sliding contact |43 effectively is a short circuit for the coaxial line which includes upper tubular member I4 I. The tuning mechanism includes tuning knob |44, a non-magnetic driving screw |45, a shaft |46, the lower end of which terminates in the upper end of movable cylindrical ange |41 and is welded thereto, and metal bel lows |48. Tuning shaft |46 is insulated from annular cap |34 and is centrally positioned by ceramic insulator |43 which is concentric and coaxial with inner casing |33 and outer shell |3|.

The upper end of bellowsv |46 is brazedto the lower end of movable flange |47 while the lower end of the bellows is 4brazed toupper pole piece ||2 at |53 and I5I, respectively. Sliding contact |43 is supported in position by tubular member |52, the upper end of whichis welded to movable flange |48. Well |53 is proportioned so as to allow the desired degree of vertical travel of sliding contact |43.

The tuning mechanism is centrally positioned by ceramic mounting yoke |54 which is attached to outer ceramic shell |3| by studs |55 and |55 respectively. Since the non-magnetic screw |45 is fastened to the tuning knob, it either raises or lowers shaft |46 because of the threaded engagements |51 and |58, which are of opposite pitch. When tuning knob is rotated in one direction, it moves downward because of threads |5'I and at the same time the tuning shaft moves downward with respect to the tuning knob because of thread |56. Thus, both movements combine to move shaft |46 downwards. Bellows I 48, therefore, is lowered, which in turn causes the sliding contact |43 to move down, thus tuning the magnetron. The output of the magnetron is coupled to wave guide |59 from the coaxial line which includes lower tubular member |42.

In order to prevent leakage of electromagnetic energy from the interaction space between bars |21 and cathode 22, cylindrical chokes are provided in the usual manner as illustrated at |58,

IBI, |62 and |63.

Water or other liquid cooling of the anode structure may -be effected by the provision of rigidi niet pipe |64 and drain pipe |65 which is centrally positioned within cylindrical casing member |40 and is coaxial therewith. As here shown, the cooling liquid spirally circulates within cylindrical casing |40 along spiral fluid channel |66 and the overflow is removed through drain pipe |65. Thus, at all times a jacket of water is provided to dissipate the heat generated in the anode structure. Similarly, in order to cool sliding contact |43 water or other cooling liquid is made to circulate within tuning shaft |46 by means of inlet pipe |61 and overflow pipe |68.

While the invention has been described with reference to several particular embodiments, it will be understood that various modications of the apparatus shown may be made within the scope of the following claims.

What is claimed is:

1. A magnetron comprising a. cylindrical housing having top and bottom end plates, an anode, means extending between said top and bottom plates and coaxial with said housing for supporting said anode, said anode comprising' axially aligned upper and lower annular discs spaced from each other and having oppositely positioned sets of bars extending toward each other from the outer periphery of said annular discs, the inner periphery of said discs being mounted on said supporting means to centrally position said anode coaxially within said housing, and a cathode girdling said anode and within said housing.

2. A magnetron comprising a cylindrical housing having top and bottom end plates, a longitudina] tubular member disposed concentrically within said housing between said top and bottom plates, an anode including axially aligned upper and lower annular discs spaced from each other and having oppositely positioned sets of bars extending toward each other from the outer periphery of said annular discs, the inner periphery of said discs being mounted on the outer Asurface of said tubular member to centrally position said anode with respect to said cylindrical housing, a cathode girdling said anode and radially spaced from said bars. and means adjacent said cathode for producing an effective uniform magnetic eld in the proximity of said anode.

3. A magnetron device comprising a cylindrical housing having top and bottom end plates, a tubular member disposed coaxially within said housing between said top and bottom plates, an anode mounted on said tubular member coaxially within said housing, said anode comprising axially aligned upper and lower annular discs spaced from each other, a plurality of bars interleaving with each other, said bars being mounted on the outer periphery of each of said upper and lower discs, and a cathode coaxially around said bars and radially spaced therefrom.

1i. A magnetron comprising a cylindrical housing having top and bottom end plates, a longitudinal tubular member disposed coaxially within said housing between said top and bottom plates, an anode comprising axially aligned upper and lower annular discs spaced from each other and having oppositely positioned sets of bars extending toward each other from the outer periphery of said annular discs, the inner periphery of said discs being mounted on the outer surface of said tubular member to centrally position said anode with respect to said cylindrical housing, a cathode girdling said anode and radially spaced from said bars, a cylindrical channel housing supporting said cathode. in position with respect to said anode, sleeves of quarter wavelength depthprojecting inwardly from each of said end plates coaxially with said tubular member and having an inner diameter greater than said tubular member, and a coaxial output tube positioned within said tubular member and extending through said top end plate.

5. A magnetron in accordance with claim 4 wherein the bars interleave with each other.

JOSEPH F. HULL.

REFERENCES CTED The following references are of record in the lle of this 4patent:

UNITED STATES PATENTS Number Name Date 2,463,416 Nordsieck Mar. l, 1949 2,482,495 Laidig` Sept. 20, 1949 2,501,354 Pease Mar. 21, 1950 '2,522,184 Ludi Sept. 12, 1950 

